多线程 锁的有关问题？

void funcB(int i)  {  if (!list.Contains(i))  {     lock (dummyObject)     {    [color=#FF0000] if (!list.Contains(i))[/color]       {         list.Add(i);         System.Diagnostics.Debug.WriteLine(i);        }     }  }  else  {  System.Diagnostics.Debug.WriteLine(i.ToString() + " existed");  }  }
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God..

失误，

在lock 里 还判断一次，

if (!list.Contains(i))
{
}
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dummyobject  

你锁这个变量，和你的list 集合是什么关系。同一个类下面？

是否是 private static object dummyobject=new object();

list 又是什么访问级别。
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C# code
Thread t1 = new Thread(new ThreadStart(FunA));            t1.Start();            Thread t2 = new Thread(new ThreadStart(FunA));            t2.Start();            Thread t3 = new Thread(new ThreadStart(FunA));            t3.Start();            Thread t4 = new Thread(new ThreadStart(FunA));            t4.Start();            Thread.Sleep(3000);            Console.WriteLine("the length of lists is {0}", lists.Count);            Console.WriteLine("the elements of lists are:");            foreach (int i in lists)            {                Console.Write(i.ToString() + " ");            }            Console.ReadLine();public static void FunA()        {            Random rand = new Random();            FunB(rand.Next(1, 10));        }        public static void FunB(Int32 i)        {            Console.WriteLine(i);            if (!lists.Contains(i))            {                lock (lockObject)                {                    if (!lists.Contains(i))                    {                        lists.Add(i);                    }                }            }        }